The Encyclopedia Americana (1920)/Butterfly
BUTTERFLY, one of the day-flying Lepidoptera of the sub-order Rhopalocera (compare Moth). This group is distinguished from the moths by the slender, knobbed antennae, which are never hairy or pectinated. The body is small, but there is a greater equality in the size of the three regions (head, thorax and abdomen) than in the moths, the abdomen being much shorter and smaller, as a general rule, than in the lower families of Lepidoptera. The ocelli are usually wanting; the spiral tongue is long, and the broad wings are carried erect when in repose, and are not held together during flight by a bristle (frenum) and socket as in most of the moths.
The caterpillars (larvæ) vary greatly in shape and in their style of ornamentation, but they uniformly have, besides the thoracic legs, five pairs of abdominal legs. The pupa is called a “chrysalis” or “aurelian,” from the bright golden hues that adorn it in many species, but disappear as the wet tissues beneath the pupa-skin harden, just before the fly appears. A few species, such as those of the genus Vanessa, hibernate, while several species, such as V. antiopa, are social as young larvæ. Butterflies also occasionally swarm while in the perfect state, such as species of Colias, Cynthia and Danais, multitudes of which are sometimes seen passing overhead in long columns. One of the North American species, and others elsewhere, are migratory, flying southward in autumn.
Butterflies are found in all parts of the world except the coldest, wherever plants exist suitable for food for the caterpillars, but they are most numerous both in species and in individuals within the tropics, and especially in South America. About 13,000 species have been described, and it is believed that twice or three times this number are in existence. About 1,000 species inhabit North America. Butterflies are especially liable to local variation, and to seasonal and dimorphic changes, so that entomologists have recorded many sub-species and temperature-forms.
Certain Nymphalidæ have glands at the end of the body secreting a repulsive fluid (see Mimicry); in others there are remarkable differences between the sexes; in certain butterflies (Androconia) some of the scales are battledore-shaped, and secrete a special odor. The species of Ageronia, a South American genus, make a clicking noise when flying. While caterpillars are plant-eaters, those of several Lyctenidæ are known to be carnivorous, feeding on plant-lice and scale-insects.
The eggs of butterflies have a membranous shell, and exhibit much variety in form and character of surface. “Sometimes,” says Holland, “they are ribbed. Between these ribs there is frequently found a fine network of raised lines, variously arranged. Sometimes the surface is covered with minute depressions, sometimes with a series of minute elevations variously disposed.” The color is most often greenish white, but many are brightly colored, or have lines and dots of color. Another peculiarity is the minute opening (micropyle) in every egg, by which the spermatoön may enter. The eggs are laid by the female on a plant that will afford suitable food for the caterpillar when it hatches. They may be deposited singly or in small or large masses; and those that will not hatch until after the following winter are protected in some way, as by a varnish, or otherwise, against the weather. Some butterflies are “single-brooded,” others lay eggs twice or more in a season, the early layings hatching quickly and the last lot surviving the winter to establish the species in the succeeding spring. Few adult butterflies survive the advent of the cold season in the North, the species continuing through the survival of eggs, larvæ or pupæ, the last sometimes by burial in the ground.
The caterpillars of butterflies are typically cylindrical and worm-like in form; but some are short and slug-shaped, or irregular in outline. The head is distinct, often large and formed of hard (chitinous) material; and often it bears horn-like projections or protrusile appendages. The thin skin is in many cases brightly ornamented with colors similar to those worn later by the adult fly (imago); but green and gray prevail — tints inconspicuous among the leaves and grasses on which most of the species feed. Most caterpillars live solitary lives; but in some species they are gregarious, and even weave large silken dwelling-places in which they live as a colony.
Caterpillars are able to grow by sloughing the skin, which from time to time cracks, enabling the creature to crawl out of it, and to begin another period of growth with a new and elastic skin that has formed beneath the old one. Four or five of these molts take place as a rule. When the larva is to hibernate, it usually does so after the first or second molt, and resumes feeding and growth when it wakes up in the spring.
One great distinction between moths and butterflies lies in the form and structure of the pupa — that quiescent stage of development in which the caterpillar is transformed to the imago. The term chrysalids is usually applied to the pupæ of butterflies, because no such a cocoon as is common among moths enwraps them. They are naked and hang free from the underside of some support, as a twig or stone, or are suspended against a surface, as the bark of a tree-trunk, attached to a “button” of silk, and held in place by a girdling thread of silk. Chrysalids are usually protectively colored.
The families of butterflies are few, and all of them, except one small tropical group (Libytheidæ) are represented in every continent. Following is a list of the five families recognized by American entomologists, beginning with the most primitive and ending with the most specialized: (1) Hesperiidæ, (2) Papilionidæ, (3) Lycænidæ, (4) Lemoniidæ, (5) Nymphalidæ. In the last three families, which comprise the majority of butterflies, the first pair of legs is more or less modified, differing from the two hinder pairs, especially in the male nymphalids, in the more or less aborted tarsi, or toe-joints.
The Hesperiidæ, or “skippers,” have a world-wide range except New Zealand, and are largely represented in the United States. This family contains small, prevailingly brown butterflies, with relatively large bodies and broad heads, the feelers hooked at the tip. The forewing is triangular and pointed in shape and the prevailing color is brown. The hesperiids are remarkable for their short, jerky flights. The pupa is enclosed in a light, silky cocoon.
The Papilionidæ are a very populous family of large and handsome butterflies, familiarly called “swallow-tails” from the prolongation of the hind wing in many of them. Yellow is a prevailing color, usually ornamented with black, red-brown or some other dark tint. The wing-neuration differs characteristically from that in other families. All six feet are present in both sexes. The caterpillar is cylindrical, elongate and never hairy, but often tuberculate and is provided with a retractile tentacle behind the head, which in some species emits a highly disagreeable odor of protective value. The pupa has two anterior projections called “nosehorns,” and hangs to its food-plant by its anal extremity, sustained by a loose girdle. This family is distributed throughout the world.
The Lycænidæ are a very large family of small or moderately sized butterflies with slender bodies, the feelers placed close together, and the front feet aborted in the males. The caterpillars are short and hairy, resembling woodlice in shape. The pupa has a well-marked "waist," is clothed with hairs or bristles, is attached to a pad of silk by the cremaster and is girdled with a silken thread. This family occurs in all parts of the world, and its members are known, on account of their prevailing hues, as “blues,” “coppers” and “hair-streaks.” In alighting they always fold their wings upright.
The Lemoniidæ are a small family related to lycænids, which contains brilliant butterflies mostly confined to tropical America, a few bright-brown species, the “metal-marks” of the subfamily Erycininæ, occurring in the southwestern United States.
The Nymphalidæ embrace a group called "four-footed" or "brush-footed" butterflies, because the foremost pair of feet in both sexes are dwarfed, hairy and held folded up against the body. This is the largest and most prominent of butterfly families, is very ancient and is much subdivided in classification. The caterpillars vary much in form, and some are hairy, or armed with spines or tubercles. The pupa hangs by its “tail,” but is not sustained by a silken girdle-thread. The nymphalids are represented in all countries but most numerously and strikingly in tropical America.
Bibliography.— Chapman, T. A., ‘Pupæ of Moths’ (in ‘Transactions’ of the Entomological Society, London 1893); Doubleday and Westwood, ‘Genera of Diurnal Lepidoptera’ (ib. 1862); Edwards, ‘Butterflies of North America’ (Philadelphia 1868-88); French, G. H., ‘Butterfles of the Eastern United States’ (Philadelphia 1895); Holland, W. J., ‘The Butterfly Book’ (New York 1898); Kellogg, ‘American Insects’ (Now York 1908); Kirby, W. F., ‘Butterflies and Moths of Europe’ (London 1907); Longstaff, ‘Butterfly Hunting in Many Lands’ (New York 1912); Miller, ‘Butterfly and Moth Book’ (ib. 1912); Packard, A. S., ‘Text-Book of Entomology’ (ib. 1898); Scudder, S. H., ‘Butterflies of New England’ (3 vols., Cambridge 1889); id., ‘Butterflies, Their Structure, Changes and Life Histories’ (ib. 1881); Strecker, ‘Butterflies and Moths of North America: Diurnes’ (Reading, Pa., 1878); Walker, ‘British Museum Catalogue of Lepidoptera’ (London 1854-56); Wood, ‘Butterflies’ (New York 1910); also the works of Boisduval, Haebner, Elmer, Moore, Niceville and Standinger.
|1 Amblypodia Amantes||3 Morpho Cypria|
|2 Ornithophera||4 Ornithophera Priamus|
|5 Papilio Hector|
|1 Mulberry Silkworm, Caterpillar and Adult||3 Chinese Silk Moth|
|2 South American Silk Moth||4 Ailanthus Moth|